I had a Purple Coral Banded Shrimp that looked pretty cool. The only problem was that I only saw it a handful of times in the middle of the night. Very secretive little shrimp!
Not so rare but I would suggest an anemone shrimp. They are clear with white or pink spots. Will stay out in the open in their anemone so you can watch and even feed them. As with most shrimp try to get a small one as most have a short life span.
now this is my type of thread! I have two more that I need to take pictures of (ones been missing so I'm not sure if he's alive :/ but I'll get them tomorrow!)